1. Field of the Invention
The present invention relates to a heat exchanger and a method for manufacturing the same, wherein tubes and fins are joined together mechanically by deforming the tubes plastically so as to increase cross-sectional areas of the tubes (hereinafter, this operation is referred to as xe2x80x9ctube enlargementxe2x80x9d).
2. Description of the Related Art
In a heat exchanger in which tubes and fins are joined together mechanically, as the tubes are deformed plastically so as to increase the cross-sectional areas of the tubes by tube enlargement, tube material must have a relatively large elongation rate and, at the same time, it must be resistant to elongation. Therefore, conventionally (for example, in Japanese Unexamined Patent Publication No. 2000-74589), seamless tubes that are seamless and manufactured by drawing or extrusion processes are adopted as the tubes for the tube enlargement.
Here, it should be noted that the seamless tubes have a higher production cost than welded tubes (tubes manufactured by bending plate material in a tubular manner and then joining seams by welding) as the seamless tubes take more man-hours (thus have a higher production cost) than the welded tubes.
Therefore, the inventors of the present invention have studied to adopt the welded tubes in place of the seamless tubes in the heat exchanger in which the tubes and the plate fins are joined together mechanically, but, as welds in the welded tubes are softened due to heat at the time of welding in comparison with tube material (regions other than the welds) and have lower proof stress (mechanical strength), it is difficult to simply replace the seamless tubes with the welded tubes.
In view of the above problem, it is an object of the present invention to join tubes and fins together mechanically by tube enlargement in the case of using welded tubes.
In order to achieve the above object, according to an aspect of the present invention, there is provided a heat exchanger having tubes (111) through which fluid flows, and fins (112) for promoting heat exchange between one fluid flowing through the tubes (111) and air passing between the tubes (111), in which the tubes (111) and the fins (112) are joined together mechanically by deforming the tubes (111) plastically so as to increase cross-sectional areas of the tubes (111) in a state in which the tubes (111) are inserted through insertion holes (112a) provided in the fins (112), wherein the tubes (111) are welded tubes manufactured by bending plate material to form flat tubes and then joining seams by welding, and welds (111a) of the tubes (111) are provided in areas that are offset from curved portions (111b) formed at the ends in the length direction.
According to this aspect, as the welds (111a) are provided in the areas that are offset from the curved portions (111b) where stress concentration is likely to occur, excess stress occurring at the welds (111a) at the time of tube enlargement can be inhibited.
Therefore, even if the welds (111a) are softened and proof stress (mechanical strength) is reduced at the time of welding, as the stress occurring at the welds (111a) at the time of the tube enlargement can be prevented from exceeding the proof stress (allowable stress) of the welds (111a), the welded tubes can be adopted in the heat exchanger in which the tubes (111) and the fins (112) are joined together mechanically. As a result, the manufacturing cost of the tubes 111 can be reduced in comparison with the case when the seamless tubes are adopted as the tubes (111).
According to another aspect of the present invention, the welds (111a) are provided in areas that substantially correspond to a center position in the length direction.
Therefore, as the stress occurring at the welds (111a) can be reduced reliably, the reliability of the tubes (111) can be improved further.
According to still another aspect of the present invention, depressions (112d) that are depressed in the direction of padding of the welds (111a) are provided in areas of edges of the insertion holes (112a) that correspond to the welds (111a).
In this aspect, as the depressions (112d) act as relief means for mitigating interference between the padding and the insertion holes (112a), clearances created between the tubes (111) and the fins (112) in the vicinity of the padding are reduced in comparison with the case in which the depressions (112d) are not provided.
Therefore, as contact areas (thus heat conduction) between the tubes (111) and the fins (112) can be prevented from being reduced, heat exchange capacity can also be prevented from being reduced.
According to yet another aspect of the present invention, there is provided a heat exchanger having tubes (111) through which fluid flow, and fins (112) for promoting heat exchange between one fluid flowing through the tubes (111) and air passing between the tubes (111), in which the tubes (111) and the fins (112) are joined together mechanically by deforming the tubes (111) plastically so as to increase cross-sectional areas of the tubes (111) in a state in which the tubes (111) are inserted through insertion holes (112a) provided in the fins (112), wherein the tubes (111) are welded tubes manufactured by bending plate material in a tubular manner and then joining seams by welding, and depressions (112d) that are depressed in the direction of padding of the welds (111a) are provided in areas of edges of the insertion holes (112a) that correspond to the welds (111a).
In this aspect, as the depressions (112d) act as relief means for mitigating interference between the padding and the insertion holes (112a), clearances created between the tubes (111) and the fins (112) in the vicinity of the padding are reduced in comparison with the case in which the depressions (112d) are not provided.
Therefore, as contact areas (thus heat conduction) between the tubes (111) and the fins (112) can be prevented from being reduced, the heat exchange capacity can also be prevented from being reduced.
Here, it is to be noted that the application of the present invention is not limited to the flat tubes, but it can also be applied to tubes of other shapes such as circular tubes and so on.
Further, according to the present invention, there is provided a method for manufacturing a heat exchanger, comprising the steps of: providing slits (210) for avoiding interference with padding in areas of tube enlargement jigs (200) for enlarging tubes (111) that correspond to the padding of the welds (111a), wherein a slit width (D) of the slits (210) is larger than a padding width (d) of the welds (111a) and a ratio (D/A) of the slit width (D) to a dimension (A) of areas that are parallel to the slit width (D) among outside dimensions of the tube enlargement jigs (200) is 0.32 or less; and joining the tubes (111) and the fins (112) mechanically by deforming the tubes (111) plastically by using the tube enlargement jigs (200).
Therefore, as shown in FIG. 17 described below, the tubes (111) and the fins (112) can be joined mechanically without reducing the heat dissipation capacity significantly.
Here, it is to be noted that reference numerals within parentheses attached to each means described above are shown exemplarily for indicating a relationship with specific means in the embodiments described below.
Hereinafter, the present invention will be more fully understood from the following description of the preferred embodiment thereof taken together with the accompanying drawings.